The present invention relates, in general, to chemical etching and, more particularly, to chemical etching of titanium-tungsten (TiW) and/or titanium-tungsten-nitride.
Many methods of chemical etching are known in the art. Generally, a solution of EDTA (ethylenediaminetraacetic acid), hydrogen peroxide (H.sub.2 .sub.O2), and ammonium hydroxide (NH.sub.4 0H) is used in the etching of titanium-tungsten. However, two problems exist with the use of this mixture as an etchant: undercutting; and differing etch rates for the TiW and TiWN. Undercutting is a problem encountered at the interface of two chemically different metals. In tape automated bonding (TAB), layers of TiW and TiWN are often used to physically coupled a gold bump to the substrate. During the etching of the TiW and TiWN, a galvanic effect causes the etchant to undercut the gold bump. This is enhanced by the presence of NH.sub.4 OH, an electrolyte. This conductive property of NH.sub.4 OH enhances the galvanic effect and increases the undercut rate of the etchant. Under normal etching conditions, it has been found that the etchant will completely undercut the gold bump before completing the etch of the TiWN layer.
The second problem is that the etch rates of TiW and TiWN differ with TiW etching faster. This contributes to the overall problem of undercut during etching.
Accordingly, it is an object of the present invention to provide a method of chemically etching TiW and/or TiWN that overcomes the above deficiencies and problems.
A further object of the present invention is to provide a method of chemically etching TiW and/or TiWN that will reduce undercut.
Another object of the present invention is to provide a method of chemically etching TiW and/or TiWN that will provide a more uniform etch.
The above and other objects and advantages of the present invention are provided by the method of chemically etching TiW and/or TiWN described herein.